1. Field of the Invention
The present invention relates generally to battery power for electrical devices, and, more particularly, to enhancing battery operation of portable electrical devices.
2. Description of the Prior Art
Presently, the performance obtainable from various different types of portable devices, such as laptop or notebook computers, cellular telephones, and video cameras, depends crucially upon electrical performance of batteries. In such applications, conventional batteries impose a number of limitations including being an unreliable source of electrical power. For example, conventional batteries provide little advance warning that they are about to completely discharge, or any indication of remaining operating time. Furthermore, battery powered equipment cannot determine if a battery's present electrical capacity is sufficient to power an additional electrical load, such as starting a hard disk drive included in a laptop or notebook computer. Finally, conventional battery chargers must be individually tailored for a particular type of battery chemistry, e.g. NiMH, Li-ion, Lithium Polymer, etc. Attempting to recharge a battery with the wrong type of charger may damage either the charger or the battery.
Recently, a new system has been specified for use in battery powered portable devices that is identified as the System Management Bus ("SMBus"). The SMBus prescribes data protocols, device addresses, and additional electrical requirements necessary to transport commands and information among various subsystems of a battery powered device. The SMBus specification envisions the SMBus interconnecting at least a system host computer, a smart battery charger, and a smart battery that are all included in the portable device. Under the SMBus protocol, the smart battery provides data, via the SMBus, to the portable device's host computer. A power management routine executed by the host computer processes such smart battery data to manage operation of at least the smart battery and the smart battery charger.
In accordance with the SMBus specification and protocol, a smart battery accurately reports its characteristics to the host computer via the SMBus. If a portable device includes more than one battery, each battery reports such characteristics independently via the SMBus. Providing the power management routine executed by the host computer with information about the charge state of each battery permits displaying the batteries' charge states, and accurately estimating the portable device's remaining operating time. However, in addition to providing information about the batteries' charge state, the information obtained via the SMBus is sufficient to permit electrical power management for the portable device, and to also permit controlling battery re-charging regardless of a battery's particular chemistry.
To achieve the preceding objectives, the SMBus specifies that, independent of host computer power management routine operation, a smart battery charger must periodically poll a smart battery that is being recharged for the battery's charging characteristics. Upon receiving a response from the smart battery, the smart battery charger then adjusts its output to match the smart battery's requirements. To avoid battery damage, the smart battery also reports certain conditions such as over charge, over voltage, over temperature, and too rapid temperature increase to the smart battery charger. In this way the smart battery effectively controls its charging cycle. Moreover, to prolong smart battery life, the smart battery charger may prevent a fully charged smart battery from powering the portable device if a source of external electrical power is available.
Analogously, the power management routine executed by the host computer may poll the smart battery, that powers the host computer's operation, for smart battery information. The power management routine can request factual information about the battery such as the battery's chemistry, or the battery's operating temperature, voltage, or charge or discharge current. The power management routine can either display such information directly, or it may process such information for use in the computer system's power management scheme, and/or to display an estimate of the battery's operating capabilities. Similar to the smart charger, the power management routine receives information about critical events if the smart battery detects a problem. Moreover, the power management routine also receives smart battery estimates about end of discharge, electrical capacity remaining below a preset threshold value, and time remaining until discharge below a preset threshold value.
As part of the host computer's power management scheme, the power management routine may provide other routines with information about battery condition. Accordingly, the power management routine may query a device driver routine to determine if an anticipated action will endanger the host computer's electrical power integrity. For example, before attempting to start a hard disk drive the power management routine may first determine if that particular operation might cause the smart battery's output voltage to drop below a threshold for host computer failure. Under such circumstances, the hard disk device driver's response might be to increase power available for starting the hard disk drive by causing the power management routine to turn-off a non-critical power use such as liquid crystal display ("LCD") backlighting.
In addition to a smart battery and a smart charger, a portable device that implements the SMBus must also include a smart battery selector. The SMBus specification and protocol includes a smart battery selector because a portable device may include two or more smart batteries, only one of which may be in use for powering the portable device's operation at any instant in time. In such multi-battery devices, the smart battery selector must arbitrate between or among batteries. Furthermore, the smart battery selector must be capable of swiftly re-configuring the portable devices power if a battery were to be suddenly removed, such as might occur if a battery were removed from a laptop or notebook computer to install a floppy diskette drive.
The simultaneous presence of two or more batteries in a portable device imposes certain operating constraints on the smart battery selector. For example, when a portable device operates from battery power, electrical power must come only from a single battery. All other batteries must be electrically isolated from the operating battery to avoid a possibility of high-current conditions that may occur if two or more batteries having differing electrical characteristics or states are simply connected in parallel. Moreover, the smart battery selector must couple to the SMBus the battery which is supplying power to the portable device so critical battery messages may be communicated between that smart battery and the power management routine executed by the host computer. However, the smart battery selector must also permit interrogation of other batteries by the power management routine so it can determine those batteries' capacity, etc. without interfering with the normal operation of the smart battery that is powering the portable device's operation. Furthermore, the smart battery selector must notify the power management routine about changes in electrical power configuration such as removal of a battery, or connection of a battery charger to the portable device.
Operation of a portable device from an external source of electrical power imposes additional constraints upon the smart battery selector's operation in addition to those set forth above that occur during battery powered operation. For example, the electrical power output from all batteries must be isolated from the external electrical power to avoid uncontrolled electrical currents into or out of the smart batteries. If one of the smart batteries is being charged, the smart battery selector must also properly couple that smart battery's SMBus, together with a thermistor included in the smart battery, to the smart battery charger so that smart battery controls its charging cycle. Finally, upon disconnection or failure of the source of external electrical power, the smart battery selector must immediately supply the portable device with electrical power from one of the smart batteries, and concurrently notify the power management routine executed by the host computer about the change.
Additional, more detailed information about the SMBus specifications and protocol, and about smart batteries is provided by:
System Management Bus Specification, Revision 1.0, Intel, Corporation, Feb. 15, 1995; PA0 System Management Bus BIOS Interface Specification, Revision 1.0, Intel, Corporation, Feb. 15, 1995; PA0 Smart Battery Charger Specification Revision 1.0, Duracell Inc. and Intel Corporation, Jun. 27, 1996; PA0 Smart Battery Data Specification Revision 1.0, Duracell Inc. and Intel Corporation, Feb. 15, 1995; and PA0 Smart Battery Selector Specification Revision 1.0, Duracell Inc. and Intel Corporation, Sep. 5, 1996.
The publications listed above are hereby incorporated herein by reference as though fully set forth here.
While the SMBus specification and protocol addresses many significant problems experienced with battery powered operation of portable devices, it fails to address other significant operational constraints. For example, to facilitate controlling power consumption in portable personal computers such as laptop or notebook computers, microprocessors manufactured by Intel Corporation of Santa Clara, Calif. provide a System Management Mode ("SMM") of operation. SMM in these microprocessors provides a separate environment for the execution of power management routines that is completely independent of the environment in which the operating system and application programs execute. For such microprocessors, a special system management interrupt ("SMI") activates the SMM operating environment. For example, power management routines executed in SMM in response to specific SMIs may cause the personal computer to enter a "Suspend" mode of operation operating in the "Suspend" mode, the computer consumes a lesser amount of electrical power because certain parts of the computer are turned off, e.g. the display and any back-lighting for the display, the hard disk, the modem, etc. In a particular "Suspend" operating mode, the microprocessor itself receives no electrical power. Restoring the microprocessor's operation from this extremely low power "Suspend" operating mode requires full operation of a hard disk drive included in the computer, and retrieval from the hard disk of data essential to restoring and resuming computer program execution. However, if the host computer included in laptop or notebook computer begins operating in its lower power; "Suspend" operating mode, the power management routine cannot detect or respond to SMBus messages from the smart battery that powers the host computer's operation. Consequently, under such circumstances the host computer's power management routine will miss or loose SMBus messages from the smart battery which seek to inform the power management routine that the battery which powers the computer's operation is about to become discharged.
Another nuisance associated with many battery powered devices, such as laptop or notebook computers, is the need to carry a AC-DC converter that is separate from the computer itself. Such battery powered devices require an external AC-DC converter so they may operate from an external power source, and for recharging the laptop or notebook computer's batteries.